The invention relates to an absorption refrigerating machine and a method for its operation. It may be used as a domestic cooling appliance, for example as the last link in the cold chain, or for cooling medicines, or as a cooling set in an air conditioning system, its use being possible as a stand-alone variant without connection to an electrical power supply.
In sorption refrigerating machines it is known that gases or vapours are bound under certain conditions to another material (solvent) and under other conditions are driven out again. The "condensation" is effected by the deposition of a pure coolant on a material partly led in a second circuit. The energy supplied to this system is used in such a way that the coolant is separated from the second medium. The heat released during the deposition can be removed to the atmosphere, whilst the energy for the separation procedure is absorbed as heat. Such a refrigerating machine has the advantage that no moving parts are required which are subject to wear or cause noise. A disadvantage is however that these machines have a lower degree of efficiency compared to the known compression machines.
A special embodiment of such refrigerating machines are absorption refrigerating machines in which the mixture comprising coolant and solvent is fed into a rectifier or ejector and, by the application of heat, is brought to boiling point. The coolant vapour thus ejected is precipitated in a condenser and the liquid resulting there cools intensely during the pressure release in the evaporator. During evaporation the heat is taken up out of the material to be cooled. The resultant vapour flows into the absorber, in which also the residual liquid from the rectifier is de-pressurised. This residual liquid trickles through the vapour and thus absorbs it. The resultant absorption heat is removed to the environment. The mixture formed from coolant and solvent is in turn passed into the rectifier and then, with renewed separation, the circuit is completed.
Further disadvantages of the known absorption refrigerating machines are pressure losses occurring between ejector and condenser, the incomplete rectification (the coolant flowing to condenser and evaporator still contains a small residual content of solvent), the incomplete evaporation due to the residual content of solvents, a further pressure loss between evaporator and absorber, and incomplete ejection and incomplete heat-exchange within the solvent circuits, and an incomplete absorption (causes supercooling of the solution) leading to a reduction in the coolant performance and thus the greatest disadvantage.
All this leads to a situation in which a relatively large amount of energy must be supplied in order to achieve a corresponding cooling effect, which, as already stated, results in a reduction in efficiency.
First experiments using solar energy showed that in particular when ammonia is used as a coolant, problems arise which do not permit such refrigeration machines to be used simply. When ammonia is used, its toxicity is a substantial disadvantage, which greatly restricts the universality of any possible use. Furthermore, pressure levels must be controlled and a special rectifier device is necessary, these likewise considerably restricting the possibilities of use.
Thus there is known from WO 88/08109 an absorption refrigerating system with a solar collector, which is intended to be postponed to particular periods of time, in order for example to utilise more favourable night current tariffs. In this absorption refrigerating machine, likewise, liquid coolant is intermediately stored. In this case storage is in liquid containers disposed in the evaporator. Thus however regulation is likewise not possible. The generation of cold depends on the capacity of the evaporator and the quantity of liquefied coolant which is generated and which can be stored. In this refrigerating machine it is also suggested to store absorbent agent, also incompletely, in supply spaces accommodated in the absorber.
Another absorption refrigerating machine is described in DE OS 27 19 995, which is intended to be operated continuously or periodically. This refrigerating machine is separated by means of separator valves into a high pressure and low pressure portions, which can be operated separately or in common. Storage units for coolant, the solution or absorbent agent and for solution with a high coolant content are used. In this known absorption refrigerating system it is however absolutely necessary to use pumps or condensers for transporting the solution and coolant, which impair the degree of efficiency and requires a site which has available a connection for electrical power or generation of electrical power. Moveover the different separating valves must be operated in dependence on operational condition, which requires a complex control or regulating.
Solutions for a continuous generation of cold utilising energy sources which are not permanently present, as is the case with solar energy, have however not yet been discovered in a practicable form for use a stand-alone variant.